Gaub, 27, appeared in four games for the Cubs last season and has a 3.81 ERA with 11.8 K/9 and 6.3 BB/9 across parts of four Triple-A seasons. The Rays claimed him off of waivers from the Cubs in April then stashed him at Triple-A. Robbie Ross is the Rangers' lone left-handed reliever at the moment, so Gaub provides some depth.